現(xiàn)階段的iOS應(yīng)用開發(fā)，我們必須在AppDelegate中設(shè)置self.window.rootViewController，但是在以前老版本的xcode中可以不設(shè)置，iOS應(yīng)用也可以照常運(yùn)行。因此如果一些老的項(xiàng)目或者照一些老的iOS教程書籍敲的代碼，運(yùn)行就可能會(huì)出現(xiàn)下面的異常：

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', 
reason: 'Application windows are expected to have a root view controller at the end of application launch'

并且app只能打開啟動(dòng)屏，無法進(jìn)入應(yīng)用，程序在main函數(shù)中停止運(yùn)行，如下圖所示：

norootviewcontroller.png

這里我碰到這個(gè)問題的demo是這樣的，有一個(gè)自定義view，代碼如下：

//
//  BNRHypnosisView.h
//  Hypnosister
//
//  Created by JackRo on 2017/2/21.
//  Copyright ? 2017年 JackRo. All rights reserved.
//
#import <UIKit/UIKit.h>

@interface BNRHypnosisView : UIView

@end



//
//  BNRHypnosisView.m
//  Hypnosister
//
//  Created by JackRo on 2017/2/21.
//  Copyright ? 2017年 JackRo. All rights reserved.
//

#import "BNRHypnosisView.h"

@implementation BNRHypnosisView

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor clearColor];
    }
    return self;
}

/*
// Only override drawRect: if you perform custom drawing.
// An empty implementation adversely affects performance during animation.
- (void)drawRect:(CGRect)rect {
    // Drawing code
}
*/

- (void)drawRect:(CGRect)rect {
    CGRect bounds = self.bounds;
    CGPoint center;
    center.x = bounds.origin.x + bounds.size.width / 2.0;
    center.y = bounds.origin.y + bounds.size.height / 2.0;

    float radius = (MIN(bounds.size.width, bounds.size.height) / 2.0);

    UIBezierPath *path = [[UIBezierPath alloc] init];

    [path addArcWithCenter:center radius:radius startAngle:0.0 endAngle:M_PI*2.0 clockwise:YES];

    [path stroke];
}

@end

AppDelegate中代碼如下：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];


    CGRect firstFrame = self.window.bounds;
    BNRHypnosisView *firstView = [[BNRHypnosisView alloc] initWithFrame:firstFrame];
    firstView.backgroundColor = [UIColor redColor];
    [self.window addSubview:firstView];


    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}

根據(jù)異常信息的意思，應(yīng)用就是缺少一個(gè)rootViewController，所以在AppDelegate中給應(yīng)用設(shè)置rootViewController就可以了，所以解決后的代碼如下所示：

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];

    //-----------------------------------------------------------------------------------------
    //解決該問題的代碼
    NSArray *windows = [[UIApplication sharedApplication] windows];
    for(UIWindow *window in windows) {
        if(window.rootViewController == nil){
            UIViewController *vc = [[UIViewController alloc]initWithNibName:nil
                                                                 bundle:nil];
            window.rootViewController = vc;
        }
    }
    //解決該問題的代碼
    //----------------------------------------------------------------------------------------

    CGRect firstFrame = self.window.bounds;
    BNRHypnosisView *firstView = [[BNRHypnosisView alloc] initWithFrame:firstFrame];
    firstView.backgroundColor = [UIColor redColor];
    [self.window addSubview:firstView];


    self.window.backgroundColor = [UIColor whiteColor];
    [self.window makeKeyAndVisible];
    return YES;
}